Introduction

The anterior cruciate ligament (ACL) is one of 2 cruciate ligaments which aids in stabilization of the knee joint. It is a strong band made of connective tissue and collagenous fibers that originate from the anteromedial aspect of the intercondylar region of the tibial plateau and extends posteromedially to attach to the lateral femoral condyle. The anteromedial bundle and posterolateral bundle form the 2 components of the ACL. [1][2][3] The ACL and the posterior cruciate ligament (PCL) together form a cross (or an “x”) within the knee and prevents excessive forward or backward motion of the tibia in relation to the femur during flexion and extension. The ACL additionally provides rotational stability to the knee with varus or valgus stress. ACL sprains and tears are common knee injuries with a reported incidence of 100,000 to 200,000 in the United States every year.

Etiology

The ACL is the most commonly injured ligament in the knee. The annual reported incidence in the United States alone is approximately 1 in 3500 people. However, data may not be accurate as there is no standard surveillance. Most ACL tears occur in athletes by noncontact mechanisms versus contact mechanisms, such as rotational forces versus a direct hit to the knee. The most at risk athletes for noncontact injury include skiers, soccer players, and basketball players, while the most at risk athletes for contact injury are football players.

Epidemiology

There is no age or gender bias; however, it has been suggested that women are at increased risk of ACL injury secondary to a multitude of factors. Some studies suggest that females may have weaker hamstrings and preferential utilize the quadriceps muscle group while decelerating. When engaging the quadriceps musculature while slowing down, this places abnormally increased stress on the ACL, as the quadriceps muscles are less effective at preventing anterior tibial translation versus the hamstring muscles. A second factor that may increase the risk of ACL injury is the increased valgus angulation of the knee. [4][5]One study utilizing video analysis demonstrated that female athletes are more likely to place their knees in increased valgus angulations when changing directions suddenly, which increased the stress on the ACL ligament. Lastly, it has been suggested that estrogenic effects on the strength and flexibility of tissues such as ligaments may play a role and predispose females to injury; however, this remains controversial and has yet to be proven.

History and Physical

One of the most common knee injuries is an ACL sprain or tear. Typically, injury occurs during activity/sports play that includes sudden changes in the direction of movement, rapid stopping, jumping and landing abnormally, a direct blow to the lateral aspect of the knee, or slowing down while running.

Most patients complain of hearing and feeling a sudden “pop” and feel that their knee “gives out” from under them at the time of injury. Other symptoms include tenderness along the joint line, pain, and swelling, decreased or loss of range of motion, and difficulty ambulating.

The physical exam should include timing of the injury, mechanism of injury, ambulatory status, joint stability, mobility, strength, palpation, and evaluation of possible associated injuries.

Multiple maneuvers are employed to test the ACL and include the anterior drawer, the pivot shift, and the Lachman tests.[6][7] These tests should be performed whenever there is suspicion for injury to the anterior cruciate ligament.

The anterior drawer test is performed with the patient lying supine with their affected knee flexed to 90 degrees and the foot in a planted position (Sometimes it is easiest for the clinician to stabilize the patient’s foot by sitting on it). The clinician will grip the proximal tibia with both hands and pull with an anterior motion. If there is excessive anterior motion and instability, then the test is positive. It may also be useful to compare to the unaffected knee as patients may have increased laxity of the ACL that is not pathologic. This test has a sensitivity of 92% and specificity of 91% in chronic injuries, but not acute injuries.

The pivot shift test is performed with the patient in the supine position. The clinician should hold the patient’s lower leg and begin with the knee in extension and flexion of the hip to 20 to 30 degrees. Next, the clinician will bring the tibia into the internal rotation with one hand and begin placing valgus stress on the knee using the other hand. While holding this position, the knee should now be flexed. This causes stress, instability, and ultimately subluxation of the ACL of the affected knee. With flexion of the knee, if the tibia subluxes posteriorly and one may feel a “clunk”; this would indicate a positive test. This test can be difficult to perform in patients who are guarding, and some may not allow the clinician to perform the test. This is a highly specific test (98%) when positive, but is insensitive (24%) due to the difficulty in evaluation secondary to patient pain and cooperation.

The Lachman test is performed with the patient in the supine position with the knee flexed to about 30 degrees. The clinician should stabilize the distal femur with one hand and with the other hand pull the tibia toward themselves. If there is increased anterior translation, then this is a positive test. Again, comparing to the unaffected side may be helpful. This test has a sensitivity of 95% and specificity of 94% for ACL rupture.

It is important to evaluate for associated injuries such as medial or lateral collateral ligamentous injury, injury to the posterior collateral ligament, or meniscal injuries.

Evaluation

Although ACL injury can be diagnosed clinically, imaging with magnetic resonance (MRI) is often utilized to confirm the diagnosis. MRI is the primary modality to diagnose ACL pathology with a sensitivity of 86% and specificity of 95%. Diagnosis may also be made with knee arthroscopy to differentiate complete from partial tears, as well as chronic tears. Arthrography is considered the gold standard as it is 92% to 100% sensitive and 95% to 100% specific; however, it is rarely used as the initial step in diagnosis as it is invasive and requires anesthesia.

On MR, ACL tears have primary and secondary signs. Primary signs will indicate changes associated directly with the ligamentous injury while secondary signs are changes that are closely related to the ACL injury. Primary signs include edema, an increased signal of the anterior cruciate ligament on T2 weighted or proton density images, discontinuity of the fibers, and a change in the expected course of the ACL (alteration of Blumensaat’s line). Tears usually occur within the midportion of the ligament, and signal changes are most often seen here and appear hyperintense. Secondary signs include bone marrow edema (secondary to bone contusion), Second fracture (as discussed below), associated medial collateral ligament injury, or anterior tibial translation of greater than 7 mm of the tibia relative to the femur (best seen on lateral view).

Radiographs are generally non-contributory for ACL injuries but are helpful to rule out fractures or other associated osseous injuries. In younger patients, avulsion of the tibial attachment may be seen. Other non-specific features that can be seen on radiographs include:

Second fracture: An avulsion fracture at the site of the lateral capsular ligaments/IT band insertion on the tibia

Arcuate fracture. An avulsion fracture at the proximal fibula at the site of the lateral collateral ligament and/or biceps femoris tendon

Joint effusion

Deep lateral sulcus sign: A notch on the lateral femoral condyle with a depth of 1.5 mm or more, best seen on the lateral view

Computed tomography (CT) is not generally utilized in evaluating the ACL and is only accurate in detecting an intact ACL.

Treatment / Management

Acute treatment consists of the “RICE” therapy, which includes rest, ice, compression of the affected knee, and elevation of the affected lower extremity. Patients should be non-weight bearing and may utilize crutches, or a wheelchair if necessary. Pain relief can be achieved with over the counter medications such as NSAIDs but is typically at the discretion of the treating physician.

ACL injuries, depending upon their severity, can be managed nonoperatively or operatively. The patient with an anterior cruciate ligament injury should be referred to the orthopedic physician to discuss treatment options and a physical therapist (PT) for rehabilitation.

Nonoperative treatment is typically reserved for those with low functional demands, type and severity of ACL tear, and time of injury and subsequent assessment. Continued monitoring and treatment by an orthopedist and physical therapist is necessary and will only improve their functional status and stability post-injury. Of note, about half of the patients who initially choose the non-operative pathway will later choose to undergo surgical repair.

The decision to undergo operative treatment is based upon a multitude of factors such as patient’s baseline level of physical activity, functional demands, age, occupation, and other associated injuries, if present. [8][9][10]Athletes and individuals who are younger and more active tend to opt for surgical repair and reconstruction. Other candidates for surgical repair/reconstruction are those with significant instability of the knee and/or multiple knee structures injured. Operative treatment is typical with a tissue graft. In a recent systematic review, 81% of those involved treated with ACL reconstruction returned to some athletic activity, 65% returned to the preinjury level of competition, and 55% of high-level athletes returned to normal play and competition. Although, it has been reported that of those who undergo surgical repair, overall 90% return to near normal functioning. The factors that may contribute to a lower percentage of return to play may be secondary to external factors such as fear of reinjury.

Pearls and Other Issues

Return to activity is variable and patient dependent. Average return to full activity and/or sports participation is estimated to be between 6 to 12 months after surgical reconstruction depending upon their progress with PT and the type of sport/activity to which they are returning. However, some studies have shown up to 18 months or more for the graft to become fully functional and incorporated. Early/premature return to activity can lead to reinjury and graft failure.

Enhancing Healthcare Team Outcomes

The diagnosis and management of ACL is made by a multidisciplinary team that includes an emergency department physician, orthopedic surgeon, sports physician, nurse practitioner and a physical therapist. The initial treatment of ACL is RICE therapy. ACL injuries, depending upon their severity, can be managed nonoperatively or operatively. The patient with an anterior cruciate ligament injury should be referred to the orthopedic physician to discuss treatment options and a physical therapist (PT) for rehabilitation. The outcomes for patients with ACL injury are good but the recovery may takes at least 3-9 months of intense physical therapy.[2][11]

Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Anterior Cruciate Ligament (ACL) Knee Injuries - Questions

Take a quiz of the questions on this article.

A 16-year-old female gymnast drops from the high bar. Her right knee buckles and she hears a pop. There is immediate pain, and by the time she is seen an hour later, her knee is swollen. She reports her knee feels "loose." Effusion is noted on exam. What is the most likely isolated injury?

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

A patient presents with a suspected acute anterior cruciate ligament (ACL) tear. She is placed in an immobilizer, given pain medication, and referred to an orthopedic surgeon. She returns with markedly increased pain and effusion. Therapeutic arthrocentesis yields 80 mL of bloody fluid. Joint fluid exam shows blood and fat droplets. What is the most likely diagnosis?

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

A 17 year old was skiing when he twisted his left knee, felt a pop and then pain and swelling; on exam his knee is swollen with decreased ROM and positive Lachman and anterior drawer tests; his diagnosis?

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

A 17-year-old female is playing soccer when she feels her left knee buckle and hears a pop as she plants her left foot to kick the ball. She complains immediately of intense pain in her left knee. The next morning, she has continued left knee pain and a sensation of instability in the joint. Based on this history alone, the most likely diagnosis is:

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Physical exams to assess for ACL tears should be done immediately following an injury so that a full exam can be done before any bleeding into the joint space occurs

Lachman Test and Anterior Drawer Test are common tests done to assess for ACL injury

All ACL tears require surgical management

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

A competitive 17 year old female soccer player ruptures her anterior cruciate ligament (ACL). She informs you that she plans on playing competitively in college as well. Which of the following treatments do you suggest?

Non-surgical management with fitted knee brace in place for 2-4 months

Non-surgical treatment with 2-4 months of physical therapy

Arthroscopic surgery

Complete bed rest for 2 weeks, followed by slow return to activity as tolerated

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Following a non-contact football injury, a provider examines the knee at 90 degrees of flexion. The examiner appreciates an increased anterior translation of the tibia on the femur. The examiner also notes that the knee does not demonstrate a posterior sag sign and a negative posterior drawer test. What knee ligament is most likely injured?

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

After being tackled heavily on the football field, a patient is unable to weight bear on his right knee. In the emergency room, his knee is swollen and aspiration reveals fresh blood. What orthopedic injury is often associated with an immediate collection of blood in the joint?

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Surgery has no effect on the strength and mass of the quadriceps muscle

Only the vastus intermedius does not recover completely

Only the vastus medialis does not recover completely

The quadriceps muscle will have difficulty in totally recovering its functional characteristics

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

A 17-year-old male sustains an injury while playing soccer. The patient states that during practice he pivoted quickly to try to "steal the ball." He felt like his left knee "gave out" and has felt weak since. The patient's physical exam demonstrates a positive Lachman test. On an initial radiograph, there is a small avulsion fracture involving the lateral aspect of the tibial plateau. What is the most likely associated injury?

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Disclaimer

The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of Surgery-Podiatry Cert Surgery. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for Surgery-Podiatry Cert Surgery, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in Surgery-Podiatry Cert Surgery, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of Surgery-Podiatry Cert Surgery. When it is time for the Surgery-Podiatry Cert Surgery board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study Surgery-Podiatry Cert Surgery.